On youtube, some twat in his review video asks why Michael is “always smiling.” Because, dumbass, he’s trying desperately to be likeable, to be like his fantasy image of his father. Vito of course was not always smiling but Michael wants to be liked so he overcompensates. He is faking it till he makes it, over his grave.
“Why this confession scene? Michael, who is always so tight-lipped”– because his conscience is killing him, dumbass. Because it’s all eating him away inside. Because he wants a miracle. Because he has sinned so terribly and nothing is working, in his earthly calculations, to save himself. His attempted good deeds (already so dangerously alloyed with fraud and pretense as they are) are backfiring on him and he cannot extricate himself either from the threat of violence nor the inevitability that he will resort to violence to extricate himself. He cannot think himself out of this cobweb and he still is unwilling to perform the contrition necessary to receive grace.